The long-term goal of this project is to understand the process of speciation through genetic analysis of closely-related species. We will use classical genetic methods to reveal the number locations, and effects of genes causing mating discrimination between Drosophila species as of genes producing interspecific differences in cuticular hydrocarbons, which serve as female matting pheromone. Applying such techniques to a variety of Drosophila groups will help us answer the following questions: 1. Are mating discrimination and cuticular-hydrocarbon differences among closely-related species due to only one or a few genes of large effect, or are several to many genes involves. 2. Where in the genome are the loci causing these forms of reproductive isolation? Are they located in similar regions among different species pairs of a group, implying genetic "hotspots" of speciation? 3. Dose sexual isolation among males and females have a similar genetic basis, or are different genes involved in the two sexes? 4. Are there consistent patterns to the genetics of sexual isolation and pheromonal hydrocarbon that apply across several groups?. 5. Are the genes involved in mating discrimination concentrated on the sex chromosomes, 1 those causing hybrid sterility and inviability 6. What role cuticular hydrocarbons play in sexual isolation between species? Although sexual isolation is one of the most potent causes of speciation, we know virtually not about its genetic basis. These studies will provide data important for understanding the origin and species and in motivating new theories of speciation. The fine-structure mapping of genes cause reproductive isolation will eventually facilitate their molecular identification, which is required a complete understanding of speciation. Our results may be relevant to understanding the original species in other animals, including humans.